Pulse modulated oscillator



Jan, 13, 1948- A. EASTON PULSE MODULATED OSCILLATOR Filed ma 21, 1945Q'IIII'LI'IIIIII.

WWQSO INVENTOR ALLAN EASTON BY ATTORNEY Patented Jan. 13, 1948 PULSEMODULATED OSCILLATOR Allan Easton, Longlsland City, N. Y., assignor toEmerson Radio and Phonograph Corporation,

New York, N.'Y., a corporation of New York Application May 21, 1945,Serial No. 595,030

3 Claims.

The object of my invention is to provide a pulse modulated oscillatorwhich may be used to produce a train of oscillations in which alloscillations, including the first, are of equal amplitude and to do thissimply, efiiciently, and economically even at high frequencies.

Various ways are known for getting constant amplitude oscillations, butthese ways become expensive with increase in frequency. The reason forthis is that the voltage across the tuning coil of an oscillator, E, isapproximately equal to where I is the current through the tuning coil, Lis the inductance of the tuning coil, and C is the shunt capacity of thetuning coil and connected thereto. It is possible to make the voltagelarge by using a relatively large inductance at low frequencies. it isnecessary for various reasons to reduce the size of the inductance. Inorder to get suflicient voltage across the coil it is thereforenecessary to increase the current and such increase of current isusually expensive.

With the present invention the current I is increased by the use of athyratron tube which will draw large amounts of current momentarily, butwill remain in a ready condition while drawing something like 1milliampere.

It is therefore a further object of this invention to produce a pulsemodulated oscillator in which the oscillations of high frequency are ofequal amplitude, and of higher amplitude than obtainable by other means,using comparable input power.

In the drawing, the single figure is a circuit diagram illustrating myinvention.

The drawing illustrates my invention as applied to an oscillator whichmay operate at megacycles and in which the voltage of the constantamplitude pulse modulated oscillations may be approximately 50 volts.

In one typical embodiment of my invention it involves the use of threetubes l, 2. and 3. These are respectively, a shock tube l which may be athyratron of the 2D21 type, a clamp tube 2 which may be of the 604 type,and an oscillator 3 which may also be of the 604 type. The shock tube Ihas the well known characteristic of being able to pass a large amountof current, on the order of 2 amperes, and of rema ning in a ready statewith the passage of a small amount of current, on the order of 1milliampere. The clamp tube 2 has the well known characteristic that itsim- As the frequency goes up, however,

I pedance from cathode'to ground, which is inpatallel with the tuningcoil of the oscillator, is very high when the tube is non-conducting andvery low, on the order of 300 ohms when thetubeis conducting. Oscillatortube 3 and its circuit is permitted to oscillate, and prevented fromoscil lating by the tube 2. This occurs by reason of the fact that thetuning coil 8 is connectedinthe circuit of the tube 2 between cathodeand ground. When the tube 2 is not conducting the impedance looking intothe cathode is very high so that the tube 3 is permitted to oscillate.When the tube 2 is conducting the impedance looking into the cathode isapproximately 300 ohms and this low impedance is in shunt to theoscillator coil. Tube 3 is therefore prevented from oscillating when thetube 2 is in a conducting state.

In operation, my circuit in the ready state will be passing a smallamount of current through the thyratron l and this will charge condenser4. When it is desired to set off a train of oscillations, all of equalamplitude, a positive pulse of voltage will be applied to the grid oftube I through condenser 5 and across resistance 6, while a negativepulse of voltage will be applied simultaneously to the grid of tube 2through condenser l. Tube 2 will accordingly cease conducting and permitthe oscillator 3 to start oscillating. Tub-e I will also have itsresistance abruptly lowered so that the condenser 4 will dischargethrough the tube and momentarily pass several amperes of current throughit. This current will pass through the resistance I0 and primary l Iwhich is couoled to the oscillator coil 8. The oscillations willtherefore not have to build up from low amplitude gradually, but thefirst oscillation, due to the current in tube I, can be equal inamplitude to all of the succeeding oscillations. When the negative pulseon the clamp tube 2 ends the clamp tube begins to draw current andprovides a low resistance path in shunt to the tuning coil 8 of theoscillator, oscillations stop and the wave train ends. A small amount ofcurrent will continue to flow throu h the thyratron, maintaining it in aready state. and plate resistor 4 will be charged in preparation for thenext train of oscillations.

As may be seen from the drawing, my circuit consists of an inputterminal connected through a condenser 5 to the grid of tube l, the gridalso being connected to a 22 volt negative bias source from resistance6. The cathode of tube I is connected to ground through the resistancel0 and coil II. The anode of tube l is connected to ground through thecondenser 4. It is also connected through resistance I2 to a source ofanode voltage supply marked with the plus symbol and which will bereferred to herein as B+. 3+ is connected through resistance l3 to thegrid of tube 2 which grid is also connected to condenser 1. 3+ is alsoconnected through resistance I4 to the anode of tube 2. Thecathode oftube 2 is connected to ground through the condenser 9 in parallel withwhich is the coil 8 and. is also connected to the grid of tube 3. 3+ isconnected to the anode of tube 3 through the resistance I5. The cathodeof tube 3 is connected through the variable resistance IE to a tap onthe coil 8.

The circuit here disclosed has been tried out at a frequency of 10megacycles. The envelope of the oscillations was substantially flat andthe circuit worked well.

It will be understood by those skilled in the art that my invention iscapable of various modifications and I do not therefore desire to berestricted to the particular details shown and described but only withinthe scope of the appended claims.

What is claimed is:

l. A pulse modulated oscillator comprising a shock tube, a clamp tubeand an oscillator tube, means for operating said clamp tube to cause sad oscillator tube to oscillate and discontinue oscillating, and meanswhereby a surge of current from the shock tube is added to saidoscillations at the beginning thereof.

2. A pulse modulated oscillator comprising an oscillator tube andcircuit, a clamp tube, and a shock tube, means for operating said clamptube to start and stop the production of oscillations by said oscillatortube and circuit, and means for operating said shock tube to add currentto said oscillations at the beginning of each operation of saidoscillator.

3. A pulse modulated oscillator comprising a gaseous, grid controlledrectifier type shock tube, a clamp tube, an oscillator tube and circuit,an oscillator coil connected in the circuit of said oscillator tube andalso connected in the cathode to ground circuit of said clamp tube, asecond coil coupled to said oscillator coil, said second coil being inthe cathode to ground circuit of said shock tube.

ALLAN EASTON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,223,058 Christ Nov. 26, 19402,370,685 Rea et al Mar. 6, 1945

